Conventionally, a control device for an internal combustion engine has widely been known that performs feedback control of an air-fuel ratio of an air-fuel mixture supplied to the engine (hereinafter simply referred to as the “air-fuel ratio of the engine”) on the basis of each output value from an upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor that are respectively disposed on an upstream side and a downstream side of an exhaust passage with a three-way catalyst (hereinafter may simply be referred to as the “catalyst”) in the internal combustion engine. In such a control device, the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor detect the air-fuel ratio of exhaust gas that is discharged from each cylinder of the internal combustion engine and flows through the exhaust passage (hereinafter referred to as the “mixed exhaust gas”), and calculate an air-fuel ratio feedback amount using the air-fuel ratio detected by each of these angle sensors. Then, the feedback control is performed such that the air-fuel ratio of the engine corresponds to a target air-fuel ratio by adjusting an amount of a fuel that is injected to each of the plural cylinders on the basis of the air-fuel ratio feedback amount.
In recent years, there is a case where gasoline that is supplied to the engine as a fuel contains alcohol such as ethanol. For example, as an ethanol-containing gasoline fuel used for a so-called flexible fuel vehicle (FFV), “E3” with 3% ethanol concentration, “E85” with 85% concentration of the same, and “E100” as a 100% ethanol fuel are known, and the degrees of the ethanol concentration vary greatly. When gasoline contains alcohol, just as described, the mixed fuel of gasoline and alcohol is referred to as the “alcohol mixed fuel” or simply as the “fuel”.
Regarding the control device for the internal combustion engine in which the alcohol mixed fuel can be used, for example, Patent Document 1 below discloses a control device for a flex fuel internal combustion engine that changes a valve characteristic of an intake valve such that a flow rate of the fuel that flows into a combustion chamber via the intake valve by a variable valve mechanism is increased along with the increase in the alcohol concentration. In the conventional control device for the flex fuel internal combustion engine, a time period in which the fuel contacts the intake valve is reduced by increasing the flow rate of the fuel that flows into the combustion chamber via the intake valve, so that the fuel is suppressed from being evaporated by the heat of the intake valve. Accordingly, a detergent agent component that is added to the alcohol mixed fuel is suppressed from being extracted and deposited on the intake valve.
Also regarding the control device for the internal combustion engine in which the alcohol mixed fuel can be used, for example, Patent Document 2 below discloses a control device for an internal combustion engine that can start an engine immediately even when the alcohol mixed fuel that is difficult to be atomized in a low temperature environment is used. The conventional control device for the internal combustion engine is adopted for the internal combustion engine that includes a variable valve timing control device, determines the valve opening/closing timing of an intake valve and/or an exhaust valve according to the concentration of alcohol contained in the fuel, and atomizes the fuel by gas that is blown back to an intake passage.
There is a possibility that an intermediate product such as formaldehyde is detected as a noxious component upon combustion in the internal combustion engine in which the alcohol mixed fuel can be used. Thus, for example, Patent Document 3 discloses a valve timing control device for the engine that suppresses the discharge of formaldehyde associated with the combustion of the alcohol mixed fuel by changing the valve timing. This conventional control device includes a valve timing variable mechanism that can change the opening/closing timing of at least one of the intake valve and the exhaust valve, and the valve timing variable mechanism extends an overlap period such that a combustion temperature is increased along with the increase of the alcohol concentration in the detected fuel. In addition, for example, Patent Document 4 discloses a re-combustion control device for an alcohol engine that suppresses the discharge of formaldehyde or the like associated with the combustion of the alcohol mixed fuel. In the conventional re-combustion control device, an operation state of the engine is detected, combustion gas in another cylinder is drawn according to a partial load of the engine, and the thus-drawn combustion gas is completely combusted.